"Term seems to originate from Craigslist and/or other personal ads where the poster of the ad is in search of someone to Party (Do drugs. Usually Crystal Meth.) and Play, P&P (Engage in sex acts or intercourse.) with, just for the day/night. This term seems to be most prevalent among homosexualmen."

However, the true origin of P and P describes the act of combining Meth with other substances.

Most who use methamphetamine regularly don’t often combine the drug with other substances. However, there are a few terms that describe some of the more common combinations that some create to enhance methamphetamine use and abuse.

Examples;
Biker Coffee – Coffee and methamphetamine
Croak, Shabu – Cocaine and methamphetamine
Hugs and Kisses, P and P, Party and Play – MDMA and methamphetamine

Looking for partner to come P and P until the sun comes up twice. You host, I'll provide the P and P